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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

← All of v2.1.224 Home All releases ←olderv2.1.223 v2.1.225newer→
Claude Code v2.1.224

Cross-session messaging explains why it is unavailable

Not switched on
Useful2 Signal3
Cross-Session Messaging not in their notes

Messaging another session now tells you why it failed instead of silently doing nothing.

The refusal messages only surface once cross-session messaging is enabled, and it is off on Windows entirely.

Feature flag
tengu_harbor_kite On for this account, and not off by default

The flag server returned on for the one account this site reads, and nothing in this release compiles it off by default. The compiled default is shown below, and says which it is when we cannot read one: a fifth of gates compile in a string or a number rather than on or off, and most published releases have no gate table behind them at all. No client can see what the server returns for your account.

This account: on · anonymous baseline: on · compiled default in v2.1.224: on

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.224. It isn't a statement about your account. What a flag value here can and cannot tell you

CLAUDE_CODE_HARBOR_KITE
What

Sending a message to another session now returns a specific reason instead of quietly failing: one refusal when the feature is off in this session, another when a cross-machine send would have to route through Anthropic servers. Cross-session messaging is gated on tengu_harbor_kite (off by default) or the CLAUDE_CODE_HARBOR_KITE environment variable, and is off entirely on Windows.

Details
  • The cross-machine route additionally requires a first-party provider and that nonessential traffic is not disabled; failing either gives the second refusal.
Evidence

Cross-session messaging is not available in this session.

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.224 →